The disclosure relates generally to cooling of components, and more particularly, to a primary cooling pathway near an outer surface of a hot gas path component and a backup, secondary cooling pathway internal of the primary cooling pathway.
Hot gas path components that are exposed to a working fluid at high temperatures are used widely in industrial machines. For example, a gas turbine system includes a turbine with a number of stages with blades extending outwardly from a supporting rotor disk. Each blade includes an airfoil over which the hot combustion gases flow. The airfoil must be cooled to withstand the high temperatures produced by the combustion gases. Insufficient cooling may result in undo stress and oxidation on the airfoil and may lead to fatigue and/or damage. The airfoil thus is generally hollow with one or more internal cooling flow circuits leading to a number of cooling holes and the like. Cooling air is discharged through the cooling holes to provide film cooling to the outer surface of the airfoil. Other types of hot gas path components and other types of turbine components may be cooled in a similar fashion.
Although many models and simulations may be performed before a given component is put into operation in the field, the exact temperatures to which a component or any area thereof may reach vary greatly due to component specific hot and cold locations. Specifically, the component may have temperature dependent properties that may be adversely affected by overheating. As a result, many hot gas path components may be overcooled to compensate for localized hot spots that may develop on the components. Such excessive overcooling, however, may have a negative impact on overall industrial machine output and efficiency.
Despite the presence of cooling passages many components also rely on a thermal barrier coating (TBC) applied to an outer surface thereof to protect the component. If a break or crack, referred to as a spall, occurs in a TBC of a hot gas path component, the local temperature of the component at the spall may rise to a harmful temperature. This situation may arise even though internal cooling circuits are present within the component at the location of the spall. One approach to a TBC spall provide a plug in a cooling hole under the TBC. When a spall occurs, the plug is removed typically through exposure to heat sufficient to melt the plug, the cooling hole opens and a cooling medium can flow from an internal cooling circuit fluidly coupled to the cooling hole. The plug may be porous to assist in its removal. This process reduces overcooling. Formation of the plug however is complex, requiring precise machining and/or precise thermal or chemical processing of materials to create the plug.
Another challenge regarding cooling is addressing the situation where a particular cooling feature becomes no longer operational, or the amount of cooling required to prevent further overheating increases.